Quote:
Originally Posted by
goob
Does using the E4300 allow you to go with cheaper RAM? If the FSB doesn't need to be as high for the same OC, it should give us more options with lower rated (4200, 5300 etc) RAM modules, which will bring the system cost down as well.
I was looking at the Corsair Value Select series or similar.
It depends on the motherboard you choose and the CPU frequency you intend to achieve. A memory module DDR2-533 is guaranteed to run stably at the effective frequency 533MHz (the real frequency 266MHz; recall DDR, double data rate), DDR2-667 at 667MHz, etc. On the other hand, if you look at BIOS, you will see DRAM frequency options 400MHz, 533MHz, 667MHz and 800MHz. (The option 400MHz is found only in 945P/G motherboards.) They are not the actual DRAM frequency but merely the memory multiplier. The formula is the following:
- 400MHz = multiplier 1.5 = FSB: DRAM ratio 4:3
- 533MHz = multiplier 2 = FSB: DRAM ratio 1:1
- 667MHz = multiplier 2.5 = FSB: DRAM ratio 4:5
- 800MHz = multiplier 3 = FSB: DRAM ratio 2:3
The actual memory frequency = FSB x memory multiplier
(In GIGABYTE motherboards, multiplier is explicitly given instead of a cryptic DRAM frequency.) The default FSB is 200MHz (or 800MT/s) for E4xxx and 266MHz (or 1066MT/s) for E6xxx. (FSB is QDR, quadruple data rate, or quad pump, so MT(transfer)/s = 4 x MHz is also used.) For example, if you select FSB = 300MHz and DRAM frequency = 667MHz, the actual frequency = 300MHz x 2.5 = 750MHz, so you need DDR2-800 modules.
P965 motherboard
The minimum selectable multiplier is 2 (= DDR2-533). With this multiplier the relation between the memory speed and
the maximum theoretically possible FSB/CPU frequency is the following:
- With DDR2-533 memory
- FSB: 553MHz/2 = 266MHz
- CPU:
- 266MHz x 7 = 1.86GHz for E6300
- 266MHz x 8 = 2.13GHz for E4200 & E6400
- 266MHz x 9 = 2.40GHz for E4300 & E6600
- 266MHz x 10 = 2.66GHz for E4400 & E6700
- With DDR2-667 memory
- FSB: 667MHz/2 = 333MHz
- CPU:
- 333MHz x 7 = 2.33GHz for E6300
- 333MHz x 8 = 2.66GHz for E4200 & E6400
- 333MHz x 9 = 3.00GHz for E4300 & E6600
- 333MHz x 10 = 3.33GHz for E4400 & E6700
- With DDR2-800 memory
- FSB: 800MHz/2 = 400MHz
- CPU:
- 400MHz x 7 = 2.80GHz for E6300
- 400MHz x 8 = 3.20GHz for E4200 & E6400
- 400MHz x 9 = 3.60GHz for E4300 & E6600
- 400MHz x 10 = 4.00GHz for E4400 & E6700
P945 motherboard
The minimum selectable multiplier is 1.5 (= DDR2-400). With this multiplier the relation between the memory speed and the maximum theoretically possible FSB/CPU frequency is the following:
- With DDR2-533 memory
- FSB: 533MHz/1.5 = 355MHz
- CPU:
- 355MHz x 7 = 2.49GHz for E6300
- 355MHz x 8 = 2.84GHz for E4200 & E6400
- 355MHz x 9 = 3.20GHz for E4300 & E6600
- 355MHz x 10 = 3.55GHz for E4400 & E6700
- With DDR2-667 memory
- FSB: 667MHz/1.5 = 444MHz
- CPU:
- 444MHz x 7 = 3.11GHz for E6300
- 444MHz x 8 = 3.55GHz for E4200 & E6400
- 444MHz x 9 = 4.00GHz for E4300 & E6600
- 444MHz x 10 = 4.44GHz for E4400 & E6700
- With DDR2-800 memory
- FSB: 800MHz/1.5 = 533MHz
- CPU:
- 533MHz x 7 = 3.173GHz for E6300
- 533MHz x 8 = 4.26GHz for E4200 & E6400
- 533MHz x 9 = 4.80GHz for E4300 & E6600
- 533MHz x 10 = 5.33GHz for E4400 & E6700
Of course most P965 motherboards need a NB voltage bump for FSB over ~350MHz and most P945 motherboards cannot run at FSB over ~350MHz. And CPU itself need a voltage bump to run stably above ~2.9GHz and perhaps cannot run at above ~3.6GHz.
BTW many DDR2-667 modules except Corsair Value Select (!) are able to run at the speed of DDR2-800 (800MHz effective frequency) or more and you will have a more headroom (source:
AnandTech - Intel P965: DDR2-667 Memory Performance ).